Radio-frequency (RF) mobile communication devices typically employ power saving techniques to increase battery life. Because the transmitter power amplifier of a mobile communication device consumes a large percentage of the overall power utilized by the device, various power management systems are used to increase the overall power efficiency of the power amplifier.
One such system adjusts the transmission power of a mobile communication device in order to utilize the least amount of power necessary to maintain signal quality while minimizing interference between different wireless networks within range of the device. The use of closed automatic power control (APC) loops may be used to control power changes from one desired power level to another within the transmitter of the mobile communication device. For example, in response to receipt of a command from a cellular base station to reduce transmission power, it is known in the art to employ an APC loop between a transmitter output stage and a power amplifier of the transmitter for controlling gain and bias settings of the transmitter output stage.
Envelope tracking (ET) is another power management system known in the art, for adjusting the power supply voltage applied to the power amplifier so that the amplifier operates at peak efficiency for given instantaneous output power requirements. In operation, the voltage supplied to the power amplifier is synchronized with the envelope of the RF signal passing through the transmitter, thereby reducing unused energy that would otherwise be dissipated as heat.
In conventional envelope tracking (ET) transmitters, the gain applied to the ET signal path is scaled in response to a power step (e.g. using a table lookup) and applied to an ET modulator immediately before closing the APC loop. However, step-wise gain adjustment (scaling) of the ET signal path can result in spectral anomalies before the APC loop is closed, which persist until the APC loop has stabilized.
Reference will now be made to the exemplary embodiments illustrated, and specific language will be used herein to describe the same. It will nevertheless be understood that no limitation of the scope of protection is thereby intended.